The present invention generally relates to a biosensor. More specifically, the invention relates to a biosensor for indicating the status of a product. The invention also relates to a method of using said biosensor and a label comprising such a biosensor as well as a method of indicating the status of a product by means of the biosensor.
Said status of the product can relate to its durability or indicate to what extent the product has been cooked or heated.
In many cases, the status of a product is to a great extent a function of time and temperature.
The status may, for instance, relate to the durability of a product, such as a food or medicinal product. The product continuously changes its status such that the remaining durability continuously decreases. Normally, the product has longer durability if it is kept cool or cold. However, it is not possible to check the durability of a product only by observing the container, in which the product is packaged. Therefore such a product container is often provided with a so-called xe2x80x9cbest before datexe2x80x9d. Normally, this xe2x80x9cbest before datexe2x80x9d presupposes that the product is kept at a certain temperature, and if this temperature is exceeded the xe2x80x9cbest before datexe2x80x9d is naturally deceptive. To avoid the selling of products whose durability has expired, a xe2x80x9cbest before datexe2x80x9d is indicated, which expires with a certain margin before the expiration of the durability of the product. This means that still durable products often have to be rejected.
The status can also indicate to what extent, for instance, a food product has been cooked or heated. The product normally gets more and more cooked with increasing time and temperature. Food products can, for instance, be cooked by putting the product and its container in a microwave oven. In that case, it is not possible to check whether the food product is ready-cooked only by looking at the container, but the product is cooked by being heated for a prescribed period of time at a given effect.
Therefore, to be able to determine the status of a product in a more exact manner, different types of labels have been developed, which can be applied to product containers and which monitor the time and the temperature to which the product has been exposed and which thus indicate the status of the product stored in the container.
A first type of such labels, so-called RF tags, comprises an electric circuit with a microprocessor. The microprocessor is adapted to continuously detect and register time and temperature. By determining the status development of the product in advance as a function of time and temperature, such a label can be made to indicate the present status of the product. However, the disadvantage of such labels is that microprocessors of said type are comparatively expensive, resulting in a relatively high manufacturing cost of the labels. As a matter of fact, it is not realistic from an economic point of view to apply such labels to product containers in general, since the cost per label is too high in relation to the price of the product in each container.
A second type of labels comprises a substrate, which is adapted to provide an optically readable change, such as a change of colour, after a certain time and temperature. The optical change can be adapted to coincide with the expiration of the durability of a product. When cooking a food product, for instance when cooking food or drink in a microwave oven, such a label applied to the container can be adapted to provide an optically readable change when the product is prepared. The advantage of these labels or indicators is that they can be manufactured relatively cheap. On the other hand, the disadvantage is that the labels must be read manually. If the labels are applied, for instance, to cartons of milk, each carton of milk and the applied label must be inspected to determine the status of each of the cartons. When cooking food, a change is obtained when the food product is prepared. Thus, the label must be observed continuously to make it possible to interrupt the cooking when the food product is ready. Consequently, this type of label is rather complicated to use.
The above-described second type of labels can be designed as so-called biosensors, where an enzyme causes the desired colour change of the substrate. By using enzymes, the biosensor can be adjusted to the product whose status is to be indicated by the biosensor. Thus, it will be possible to ensure that the colour change takes place at the desired point of time while taking into account the temperature changes to which the product and the biosensor applied thereto have been exposed. However, the problem of optical reading of the result remains to be solved.
One object of the present invention is to provide an improved biosensor, which is relatively cheap to manufacture and which can be used to indicate the status of a product. The biosensor should also allow simple and rational indication of said status.
Another object of the present invention is to provide a method of using such a biosensor, a label comprising such a biosensor as well as a method of indicating the status of a product by means of such a biosensor.
To achieve the first object, a biosensor is provided in accordance with claim 1. Preferred embodiments are stated in claims 2-6.
To achieve the additional objects, a method of using said biosensor according to claim 7, a label according to claim 8 and a method according to claim 9 are stated. A preferred embodiment of the method is stated in claim 10.
More specifically, according to the present invention a biosensor is defined for indicating the status of a product, said biosensor being characterized by a unit comprising a substrate and an enzyme, which when brought into contact with the substrate is adapted to affect the substrate so that its conductivity changes as a function of time and temperature, and an electric circuit, said unit being included as a component in said electric circuit and said electric circuit being activable by applying an electric field and/or a magnetic field over the same to generate a measurable signal, which is dependent on the total resistance of the circuit.
In this way, a biosensor is provided which can be manufactured at a relatively low cost and which is very suitable for indicating the status of a product. The enzyme is suitably adapted to affect the conductivity of the substrate according to the function, according to which the status of the product is affected under the influence of time and temperature. The signal which is generated when activating the electric circuit is dependent on the total resistance of the circuit. The electric conductibility of the substrate, i.e. its conductivity which is the inverse of the specific resistance of the substrate, affects the total resistance of the circuit. Thus, the signal generated when activating the electric circuit will be dependent on the total resistance of the circuit, which in turn is dependent on the conductivity of the substrate. The signal thus also indicates indirectly, besides the present conductivity of the substrate, the present status of a product which has been exposed to the same time and temperature conditions as the biosensor. When the status development of the product under the influence of time and temperature is known, it can also be possible to make a prognosis for the future status development of the product by assuming future temperature conditions. Finally, the biosensor allows simple and rational indication of said status. The activation of the electric circuit and the reading of the generated signal can be automatized. As a result, it is not necessary to read the respective biosensors manually, whereby it is possible, for instance, to determine the status of a large number of products in an efficient manner.
The electric circuit is activated by applying an electric field and/or a magnetic field over the same. The signal which is generated when activating the circuit is preferably a measurable current induced in the circuit. The circuit is in its turn preferably a so-called oscillation circuit. Thus, a biosensor is provided, whose oscillation circuit is activable by applying, for instance, a magnetic field over the same to generate a measurable current, which is dependent on the total resistance of the circuit and which thus varies as a function of the time and temperature to which the unit of the biosensor has been exposed. As a result, indirect reading of the signal generated by the circuit is possible by reading the actual magnetic field, which is dependent on the current induced in the circuit. The current itself is dependent on the total resistance of the circuit, which resistance in turn is dependent on the present conductivity of the substrate.
According to a preferred embodiment of the inventive biosensor, the enzyme is adapted to affect the substrate so that its conductivity increases as a function of time and temperature.
The enzyme which is included in the unit of the biosensor is preferably selected from one of the following enzyme classes: Transferases, Hydrolases and Lyases. The enzyme which is currently most preferred is Urease, which is an enzyme of the enzyme class Hydrolases.
The substrate which is included in the unit of the biosensor advantageously comprises Urea. According to the present invention, use is also stated of a biosensor as defined above for indicating the status of a product, which exhibits a status development which is affected as a predetermined function of time and temperature, the enzyme being adapted to affect the conductivity of the substrate according to the same function of time and temperature, which product and which biosensor are synchronized concerning said function, the unit of the biosensor being activated by bringing the enzyme into contact with the substrate when applying the biosensor to the product, whereby the present status of the product is indicatable by applying an electric field and/or a magnetic field over the electric circuit, which, as a result, generates a signal that is dependent on the total resistance of the circuit and thus also indicates the conductivity of the substrate.
According to the invention, a label is also defined for application to a product container, said label comprising a biosensor as stated above.
Finally, according to the invention a method is defined of indicating the status of a product, such as a food or medicinal product, located in a container, comprising the steps of (i) determining the status of the product as a function of time and temperature, (ii) adapting the enzyme of a biosensor as stated above to affect the conductivity of the substrate according to the same function of time and temperature, (iii) arranging the biosensor on said container, (iv) activating the unit of the biosensor by bringing the enzyme into contact with the substrate when placing the product in the container, (v) applying an electric field and/or a magnetic field over the electric circuit when the status of the product is to be checked, (vi) measuring the signal which is in this context generated by the electric circuit of the biosensor and which is dependent on the present conductivity of the substrate, and (vii) determining on the basis of said signal the present status of the product.
According to a preferred embodiment, the method comprises the step of storing in a memory unit the measured signal together with data identifying the container on which the biosensor is arranged. This allows a quality assurance, by means of which it is possible to check afterwards to what time and temperature conditions a product has been exposed at a certain point in the handling chain.